Methods by which harmful substances, rank odors and so forth, contained in gases such as air and exhaust gases are adsorbed and decomposed to make the gases pure are known to include a method in which they are caused to chemically react with chemicals such as acid, alkali and aluminum sulfate to remove them, a method in which they are adsorbed on adsorbents such as activated carbon and zeolite to remove them, a method in which they are masked with aromatics, and a method in which they are oxidized or burnt using catalytic particles of metals or metal oxides. Methods by which substances causing rank odors, pollution, turbidity and so forth, contained in water such as river water, pond water and waste water are adsorbed and decomposed to make the water pure are also known to include a method in which they are adsorbed on adsorbents such as activated carbon and zeolite, a method in which they are oxidized and decomposed using chemicals such as ozone, and a method in which they are decomposed by microorganisms.
As methods for producing porous structural materials containing adsorbent particles such as activated carbon and zeolite or particles of metals or metal oxides having a reactivity as catalyst (catalytic activity), the following methods are conventionally known.
One of them is a method in which particles such as particles of metals or metal oxides are mixed and the mixture is press-molded (a method called press molding). For example, Japanese Patent Application Laid-open (KOKAI) No. 50-30795 discloses a method in which 40 parts by weight of manganese dioxide, 20 parts by weight of cupric oxide and 40 parts by weight of gamma alumina are mixed and the mixture is formed into tablets.
Another method is a method in which a porous carrier or a porous structural material is impregnated with an aqueous solution of salts of metals such as manganese and copper, followed by baking (a method called baking or sintering). Materials used in such a method include, for example, a deodorizer comprising A-type zeolite incorporated with manganese oxide and copper oxide (Japanese Patent Application Laid-open (KOKAI) No. 1-151938), and a deodorizer comprising a honeycomb porous carrier supported with manganese dioxide and cupric oxide (Japanese Patent Application Laid-open (KOKAI) No. 4-156854).
Other methods are also known to include a method in which the adsorbent particles such as activated carbon and zeolite and/or particles of metals or metal oxides are mixed together with a binder and the mixture obtained is extruded by means of an extruder into stated shapes, followed by heating and activation to obtain porous particulate products (a method of extrusion molding with a binder), and a method in which the particles of metal oxides or the like are kneaded into a foamable thermoplastic resin, followed by heating to blow the resin into foams, which are used as deodorizing porous structural materials (a method of foaming), and so forth.
Methods for producing sheet-like deodorizers are also known to include a method in which a deodorizer powder and a thermoplastic resin powder are sprayed onto a substrate sheet made of paper or the like, followed by heating to bring them into an integral form (Japanese Patent Application Laid-open (KOKAI) No. 61-119269), and a method in which a mixture of a deodorizing powder for gas treatment and a thermoplastic resin powder is held between two layers of sheets at least one of which is an air-permeable sheet, followed by contact bonding to bring them into an integral form (Japanese Patent Application Laid-open (KOKAI) No. 5-49850), and so forth.
In the case when deodorizing porous structural materials are produced by the above pressure molding, the particles of metals or metal oxides are so closely packed that the molded products have a low specific surface area and a poor air permeability. There is another problem that particles that tend to collapse, as in the case of activated carbon and zeolite, cannot be molded.
In the case when they are produced by baking, there is a problem that oxide layers formed and impurities formed at the time of baking because of the binder used may block up the micropores of porous carriers, resulting in a decrease in specific surface area of the porous structural materials. In the case when they are produced by sintering, it is difficult to cause metal or metal oxide particles to join to the surface of activated carbon.
In the case when they are produced by extrusion molding with a binder or foaming, particles of the deodorizer powder are covered with the binder or the foamable resin, and hence odor components cannot come into direct contact with the deodorizer powder, to cause a problem that the performance inherent in the deodorizer powder cannot be exhibited.